The heart and lungs work together to circulate oxygenated blood. However, the heart can stop due to heart attack, electrical shock, drowning, or suffocation. Consequently, oxygenated blood may not flow to vital organs, particularly the brain. Brain cells begin to suffer and die within several minutes after the heart stops circulating blood. In the event of heart pumping failure, Cardio Pulmonary Resuscitation (CPR) is often administered to temporarily sustain blood circulation to the brain and other organs during efforts to restart the heart pumping. This effort is directed toward reducing hypoxic damage to the victim.
Generally, CPR is administered by a series of chest compressions to simulate systole and relaxations to simulate diastole, thus providing artificial circulatory support. Ventilation of the lungs is usually provided by mouth-to-mouth breathing or using an externally activated ventilator. Successful resuscitation is determined primarily by the time delay in starting the treatment, the effectiveness of the provider's technique, and prior or inherent damage to the heart and vital organs.
Manual CPR as taught in training courses worldwide can be easily started without delay in most cases. When properly administered, basic CPR can provide some limited circulatory support.
Despite the widespread use of CPR, and the use of certain mechanical devices, the survival of patients reviving from cardiac arrest remains poor. Each year, more than 250,000 people die in the U.S. from cardiac arrest. The rate of survival for CPR performed out of the hospital is estimated to be about 3%; and for patients who have cardiac arrest in the hospital, the rate of survival is only about 10-15%. The practical technique of CPR has changed little since the 1960's.
Most existing computer simulations of CPR use an electrical lumped parameter model of the circulation, governed by a system of ordinary differential equations (ODEs). Various mathematical models describe the standard CPR technique and various alternative CPR techniques such as: (i) interposed abdominal compression (IAC), (ii) active compression-decompression, and (iii) Lifestick CPR. Since all these models use fixed compression rates, the resulting blood flow will generally be significantly lower than its maximum possible value.